Curable resin compositions have been widely used as various coating materials and adhering materials or in optical applications. For example, specific examples of the optical applications of curable resin compositions include protective films of information recording layers in optical information recording media, particularly optical recording media. In particular, there have been conducted investigations on next-generation high-density optical disks using a blue laser (cf. Patent Document 1).
In Patent Document 1, a urethane (meth)acrylate is used as a protective layer but since the protective film is formed as a thicker film as compared with conventional ones, hardness is insufficient only with the protective layer. Therefore, by laminating a cured product of colloidal silica fine particles and an ethylenically unsaturated compound thereon as a hard coat layer, strength and shrinkage at curing are balanced. However, such a laminate type protective film is still practically insufficient in view of cost, operability, and the like.
On the other hand, Patent Document 2 is known as a polyurethane-based organic-inorganic hybrid composition to be used for coating. However, such a composition having no radiation-curable group requires a long time of 3 days for curing and thus is not practical.
Patent Document 1: JP-A-2002-245672
Patent Document 2: JP-A-2001-64346
As mentioned above, since strength when formed as a thick film is insufficient in the radiation-curable resin compositions having transparency used as protective films for information recording media hitherto known, it is desired to develop a curable resin composition having transparency and a high adhesion as the conventional protective films have and also having a sufficient strength and a low shrinkage at curing even when formed as a thick film.